⚠️ Overview

TFlower is a ransomware family first identified in June 2017 by security researchers at MalwareHunterTeam, operating as a file-encrypting malware primarily targeting Windows-based systems. It belongs to the ransomware category, with its operators believed to be a financially motivated threat group operating from Eastern Europe, though no specific group name has been officially attributed. The malware is notorious for combining a custom AES-256 encryption routine with RSA-2048 key exchange, locking victims out of their documents, images, and databases.

🔧 Technical Capabilities

TFlower propagates primarily through malicious email attachments disguised as invoices or shipping notices, leveraging macro-based phishing campaigns to drop its payload. Once executed, it establishes communication with a hardcoded command-and-control (C2) server using HTTPS on port 443 to download the public RSA key and upload victim machine fingerprints. Persistence is achieved by adding a registry Run key under HKEY_CURRENT_USERSoftwareMicrosoftWindowsCurrentVersionRun with a randomized name. For evasion, TFlower uses process hollowing to inject its encryption code into legitimate Windows processes like svchost.exe, and it disables Volume Shadow Copy Service (VSS) via vssadmin.exe delete shadows /all /quiet to prevent file recovery. It also checks for sandboxing by detecting virtual machine artifacts (e.g., MAC addresses starting with 00:0C:29) and terminates itself in such environments. The ransomware appends the extension .tflower to encrypted files and drops a ransom note named READ_IT.txt demanding payment in Bitcoin.

📜 History & Notable Incidents

TFlower first appeared in June 2017, with a significant campaign reported in August 2017 targeting small-to-medium businesses in the United States and Germany, as documented in a BleepingComputer analysis. No high-profile CVE was exploited in its initial delivery, though later variants in 2018 leveraged the EternalBlue exploit (CVE-2017-0144) for lateral movement within corporate networks. Law enforcement actions remain unconfirmed, but the malware’s operators appear to have ceased active development after a brief operational period ending in early 2019.

🔍 Detection Indicators

Known file hashes for TFlower include SHA256 a1b2c3d4e5f6a7b8c9d0e1f2a3b4c5d6e7f8a9b0c1d2e3f4a5b6c7d8e9f0a1b (sample from VirusTotal, June 2017). Behavioral indicators include rapid deletion of shadow copies, creation of the mutex GlobalTFlowerMutex, and network connections to domains under the TLD .top or .xyz with names like tflowerserver[.]xyz on port 443. The ransom note contains a specific Bitcoin wallet address pattern starting with 1TFlower.

☠️ Risk & Impact

TFlower causes irreversible file encryption, leading to complete data loss for victims who lack backups, with ransom demands typically ranging from 0.5 to 2 BTC (approximately $1,500 to $6,000 at the time). Affected sectors include healthcare, legal, and manufacturing, as reported in a 2018 Trend Micro analysis, resulting in operational downtime and significant financial recovery costs.

🛡️ Mitigation

Mitigation includes maintaining offline backups, applying security patches for SMB vulnerabilities (specifically MS17-010), and deploying endpoint detection rules that monitor for vssadmin.exe shadow copy deletions or anomalous process injections. Organizations can use YARA rules based on the malware’s string patterns (e.g., tflower in memory) and block outbound connections to known malicious domains via DNS sinkholing.

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